It is often desirable that carpets and fabrics should exhibit a particular luster or sheen without glitter. While the degrees of luster and glitter exhibited by fibers used to make carpets and other fiber products may be rather subjective, there is no question that such qualities exist and that these qualities have a serious impact on the value of the fibers in certain applications.
Luster and glitter in a fiber can be altered, among other means, by introducing additives into the fiber. The additives, generally, must be immiscible with the polymer of the fiber and must have an index of refraction adequately different from that of the fiber polymer so that the additive will scatter light which impinges on the fiber.
Titanium dioxide has been added to nylon to control luster (U.S. Pat. No. 2,205,722), but titanium dioxide makes the fiber appear dull and "chalky" without reducing glitter or sparkle. Polyethylene (U.K. Pat. No. 1,116,202), polypropylene (U.S. Pat. No. 4,711,812) or polystyrene (U.K. Pat. No. 745,182) have also been used as luster additives for nylon. They do not adequately reduce glitter and they also make the fiber appear dull. However, they do not give the chalky appearance which titanium dioxide does. Polyethylene oxide (U.S. Pat. No. 4,540,746) used as a luster additive gives nylon fibers a desirable bright sheen, but also causes the fibers to have lower dye lightfastness than controls of nylon fibers which contain no polyethylene oxide.
Control of luster and glitter is important both for staple (crimped filaments generally having a length in the range of 4-10 inches) and for continuous filament products. "Bulked Continuous Filament" (BCF) yarns are preferably processed in a manner similar to that which has been taught in U.S. Pat. No. 4,559,196 using heated rollers for drawing the filaments and hot air or steam jets for bulking the filaments. Control of luster and glitter can be accomplished by introducing additives into filaments during the filament spinning process, but in subsequent treatment for the manufacture of BCF, there has often been a problem in using organic polymeric fiber additives such as polypropylene, polystyrene, polyethylene oxide or polyethylene because of sticky polymeric debris left on the heated draw rollers. Debris on heated draw rollers is sticky and can cause filaments to become adhered to the rollers and break, thus, disrupting the processing operation.